The present invention relates to a method for delignifying chemical pulp with oxygen and/or ozone, and with a possible peroxide additive. The present invention also relates to an apparatus for delignifying chemical pulp, as well as to a circulation system for executing the process of delignifying the chemical pulp.
Chemical pulp is commonly bleached with O.sub.2 or O.sub.3. Familiar processes either involve thick mass slurry bleaching with almost dry chemical pulp, or thin mass slurry bleaching of chemical pulp having a concentration of about 3% of dry substance. While thick mass slurry bleaching produces disadvantages in quality of chemical pulp, and thus makes it more difficult to execute the process, thin mass slurry bleaching has been uneconomical, due to required reactor size and required power consumption.